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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 639 · 40 sums
TalentJR

The method (Inside 180, outside the sum): Angle sum: ∠A + ∠B + ∠C = 180°. Exterior angle = sum of the two interior opposite angles. Right-angled triangle: longest side² = side² + side² (3, 4, 5 and 5, 12, 13 are famous sets). Sides can make a triangle only if the two shorter sides add up to more than the longest side.

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  1. 1.In a right-angled triangle, one of the other two angles is 13°. What is the third angle (in degrees)?
  2. 2.In an isosceles triangle, the two equal angles are 80° each. What is the third angle (in degrees)?
  3. 3.In a right-angled triangle, one of the other two angles is 71°. What is the third angle (in degrees)?
  4. 4.In an isosceles triangle, the angle between the two equal sides is 146°. What is each of the other two angles (in degrees)?
  5. 5.In an isosceles triangle, the angle between the two equal sides is 98°. What is each of the other two angles (in degrees)?
  6. 6.The angles of a triangle are in the ratio 3 : 3 : 4. What is the biggest angle (in degrees)?
  7. 7.In an isosceles triangle, the angle between the two equal sides is 64°. What is each of the other two angles (in degrees)?
  8. 8.An exterior angle of a triangle is 60°. One of its two interior opposite angles is 26°. What is the other one (in degrees)?
  9. 9.The angles of a triangle are in the ratio 1 : 2 : 3. What is the biggest angle (in degrees)?
  10. 10.In a right-angled triangle, one of the other two angles is 66°. What is the third angle (in degrees)?
  11. 11.In triangle ABC, angle A = 82° and angle B = 24°. What is angle C (in degrees)?
  12. 12.The two interior opposite angles of a triangle are 63° and 72°. What is the exterior angle (in degrees)?
  13. 13.An exterior angle of a triangle is 94°. One of its two interior opposite angles is 43°. What is the other one (in degrees)?
  14. 14.The two interior opposite angles of a triangle are 26° and 58°. What is the exterior angle (in degrees)?
  15. 15.The two shorter sides of a right-angled triangle are 12 cm and 16 cm. How long is the longest side (in cm)?
  16. 16.The angles of a triangle are in the ratio 1 : 1 : 2. What is the smallest angle (in degrees)?
  17. 17.In a right-angled triangle, one of the other two angles is 31°. What is the third angle (in degrees)?
  18. 18.The two shorter sides of a right-angled triangle are 36 cm and 15 cm. How long is the longest side (in cm)?
  19. 19.Can a triangle have sides of 10 cm, 21 cm and 9 cm? (a) No (b) Yes
  20. 20.The two shorter sides of a right-angled triangle are 24 cm and 7 cm. How long is the longest side (in cm)?
  21. 21.In triangle ABC, angle A = 55° and angle B = 74°. What is angle C (in degrees)?
  22. 22.In triangle ABC, angle A = 47° and angle B = 41°. What is angle C (in degrees)?
  23. 23.Can a triangle have sides of 10 cm, 27 cm and 12 cm? (a) Yes (b) No
  24. 24.Can a triangle have sides of 12 cm, 11 cm and 6 cm? (a) Yes (b) No
  25. 25.The angles of a triangle are in the ratio 2 : 2 : 5. What is the biggest angle (in degrees)?
  26. 26.In an isosceles triangle, the two equal angles are 50° each. What is the third angle (in degrees)?
  27. 27.The two shorter sides of a right-angled triangle are 15 cm and 8 cm. How long is the longest side (in cm)?
  28. 28.Can a triangle have sides of 9 cm, 9 cm and 21 cm? (a) No (b) Yes
  29. 29.In a right-angled triangle, one of the other two angles is 10°. What is the third angle (in degrees)?
  30. 30.Can a triangle have sides of 11 cm, 7 cm and 11 cm? (a) Yes (b) No
  31. 31.In a right-angled triangle, one of the other two angles is 30°. What is the third angle (in degrees)?
  32. 32.In triangle ABC, angle A = 29° and angle B = 31°. What is angle C (in degrees)?
  33. 33.In triangle ABC, angle A = 40° and angle B = 86°. What is angle C (in degrees)?
  34. 34.Can a triangle have sides of 2 cm, 12 cm and 11 cm? (a) No (b) Yes
  35. 35.The longest side of a right-angled triangle is 25 cm and one of the other sides is 7 cm. How long is the third side (in cm)?
  36. 36.The two shorter sides of a right-angled triangle are 12 cm and 9 cm. How long is the longest side (in cm)?
  37. 37.In an isosceles triangle, the two equal angles are 59° each. What is the third angle (in degrees)?
  38. 38.In an isosceles triangle, the two equal angles are 72° each. What is the third angle (in degrees)?
  39. 39.In an isosceles triangle, the angle between the two equal sides is 100°. What is each of the other two angles (in degrees)?
  40. 40.The two interior opposite angles of a triangle are 42° and 72°. What is the exterior angle (in degrees)?

Answer key

  1. 77
  2. 20
  3. 19
  4. 17
  5. 41
  6. 72
  7. 58
  8. 34
  9. 90
  10. 24
  11. 74
  12. 135
  13. 51
  14. 84
  15. 20
  16. 45
  17. 59
  18. 39
  19. No
  20. 25
  21. 51
  22. 92
  23. No
  24. Yes
  25. 100
  26. 80
  27. 17
  28. No
  29. 80
  30. Yes
  31. 60
  32. 120
  33. 54
  34. Yes
  35. 24
  36. 15
  37. 62
  38. 36
  39. 40
  40. 114

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